In recent years, functional proteins and functional peptides have gained attention as materials for pharmaceutical products, food and beverage products, and cosmetic products. In particular, collagen, which has effects of alleviating symptoms associated with bone and joint disorders, effects of making the skin beautiful, effects of osteogenesis, and other effects, as well as collagen peptide, which is a degradation product thereof, have been noted as representative examples of such functional proteins or functional peptides. Major raw materials for collagen or collagen peptide are, for example, the skin, the bones, and the tendons of fish, cows, pigs, and chicken, and jellyfish is one such raw materials. A method comprising subjecting a jellyfish to a treatment process, such as freezing, thawing, low temperature storage, and agitation so as to efficiently recover undenatured collagen from such jellyfish has been proposed (e.g., Patent Document 1 and Patent Document 2).
The recent jellyfish outbreaks in coastal areas of Japan are serious social problems and have caused tremendous damage to the fishery industry. In addition, the removal and disposal of jellyfish gathered around the water intakes of factories and power generation plants are cost-consuming. Accordingly, it is desirable that jellyfish be effectively used as a collagen raw material as described above. To date, a major type of jellyfish used as a collagen raw material has been Aurelia aurita because of its small size and liquescent properties, but a jellyfish that is large and has large water-insoluble protein content, such as Rhopilema esculenta, has not yet been effectively used.
In general, water-insoluble proteins are solubilized and the molecular weight thereof is reduced via heating treatment, acid or alkali treatment, treatment with a protease, or other means. However, some proteins that have been subjected to heating treatment may become thermally denatured, disadvantageously. When acid or alkali treatment is employed, amino acid may become destroyed, and disposal after the treatment is also cost-consuming and laborious. In addition, protease treatment requires adequate determination and regulation of temperature and pH level, so as to provide optimal conditions for an enzyme to be used. When an enzyme remains in the treated product, inactivation and removal of such enzyme become necessary.
A method of protein hydrolysis involving the use of a solid acid catalyst is known (Patent Document 3), and such method has been employed for the production of jellyfish collagen peptide (Patent Document 4). In these examples, however, soluble proteins are targeted, and water-insoluble proteins are not subjected to solubilization or molecular weight reduction.
Meanwhile, a technique for degrading a lignocellulose constituted by cellulose, hemicellulose, and lignin has been studied as a means for effective use of ligneous biomass resources, although such technique suffers from similar problems as those occurring in the case of the water-insoluble proteins described above. For example, acid saccharification and enzymatic saccharification are techniques available for lignocellulose degradation. Acid saccharification, which involves the use of sulfuric acid, is advantageous in terms of high reaction speed; however, this technique is problematic in terms of hyperdegradation of a certain product (a monosaccharide), and waste acid solution disposal is problematic in terms of environmental burdens. While enzymatic saccharification involving the use of a cellulase enzyme is advantageous in that it imposes lighter environmental burdens, cellulose has a water-insoluble, strong crystalline structure in which β-glucose molecules are polymerized via a 1,4-glucoside bond and the resulting polymers are bound to each other via a hydrogen bond. Thus, the contact area between such cellulose and cellulase enzyme is small, and the reaction speed is low, disadvantageously.